This invention relates to methods of determining the position of objects and in particular, although not so restricted, to methods of locating vehicles.
In recent years there has been a growing awareness of the possible benefits of using electronic navigation systems to position and track vehicles within an established highway infrastructure. Up until now navigation systems were designed primarily for use by ships and aircraft which, because of their ability to move unconstrained in any direction through featureless surroundings, relied solely upon information from a navigation system to determine their position accurately. The navigation systems used at sea and in aircraft, however, were unsuitable for use on land: they were too large to install conveniently in a land vehicle; and they were to expensive. However recent developments in navigation techniques, and in electronic data processing have reached a point where it is now possible to provide a vehicle location system at reasonable cost and suitable for installation in ordinary road going vehicles.
A vehicle location system may be employed to guide the driver of a vehicle to an intended destination or so that an operator can establish the location of one or more vehicles in a fleet of such vehicles. Regardless of the intended application of a vehicle location system, namely vehicle guidance or fleet control, the most important requirement of the system is the establishment of the position of the vehicle within acceptable limits of accuracy.
The present invention seeks to provide a vehicle location system which provides an indication of the position of a vehicle with a relatively high degree of accuracy.